COASTAL ENVIRONMENTS Lessons - PowerPoint Presentation

Slide1

COASTAL ENVIRONMENTS

Lessons

1

to 2Slide2

Defining ‘Coast’ and Waves

Lesson Objectives

1) Know what is meant by term the ‘coast’.

2) Understand waves.

Success Criteria

)Define ‘coast’.

2)Draw an accurate annotated wave diagram.Slide3

Starter:

What is the coast? In pairs come up with a definition.

Definition of the coast

: a narrow zone where the land and sea overlap and directly interact.

Factors affecting coasts: see next diagramSlide4

Factors affecting coasts:Slide5

Defining ‘Coast’ and Waves

Lesson Objectives

1) Know what is meant by term the ‘coast’.

2) Understand waves.

Success Criteria

1)Define ‘coast’.

2)Draw an accurate annotated wave diagram.Slide6

Homework for next week!

Read

Geofile

297 Basic coastal processes and make detailed notes using sub headings for next week.Slide7

Waves

Wave formation:

Transfer of energy from wind blowing over water

Tsunamis are an exception

Increase wind strength causes increased frictional drag which creates larger waves

Local waves caused by wind are known as

sea

waves, whereas waves travelling from distant storms are

swell

waves

Wave energy depends on 3 factors:

wind velocity

, period of

time

over which wind has blown,

fetchSlide8

Waves (continued)

Fetch

is the maximum distance of open water over which the wind has blown, so large fetches (e.g. across the Atlantic from SW to NE) produce high energy waves. Waves hitting parts of SW England have a fetch of 6000+KmSlide9

Waves (continued)

Wave terminology: (see handout)

Make sure you know the definition of:

Swell waves

Sea wavesFetch

Wave height

Waver period

Wave length

Wave steepness

Wave energySlide10

Waves (continued)

Swell waves

- result from distant storms and strong winds. These waves can travel long distances. Characterised by waves with low wave height, gentle steepness, long wave length, and long period.

Sea waves

- result from local wind and therefore only travel short distances. Opposite characteristics to swell, occurring in higher energy waves.

Fetch

- maximum distance of open water over which waves can develop. Longer fetch leads to more wind and waves with higher energy.

Wave height

(H) - the vertical distance between the wave crest, and the trough

Wave period

(T) - time taken for a wave to travel one wavelength.

Wave length

(L) - the distance between 2 successive crests.

Wave velocity

(C) - the speed of movement of a wave.

Wave steepness

(H÷L) - ratio of wave height to wave length, cannot exceed 1:7, or wave will break.

Wave energy

(E) - the energy possessed by a wave in deep water expressed as EµLH2. Slide11

Waves (continued)

Waves in deep water:

Deep water = when

depth is > than one-quarter of the wave lengthWind drag on the sea surface causes water to move in an

orbital motionWaves are surface features – the size of orbits decreases with depthSlide12
Slide13

Waves (continued)

Waves in shallow water:

Water is ‘shallow’ when the depth is less than one-quarter of the wave length

Friction with the seabed increasesAs the base of the wave slows down, the circular oscillations become ellipticalSlide14

Waves (continued)

Waves in shallow water:

Water is considered shallow if

D<½L

In shallow water friction with the sea bed increases and as the base of the wave slows downThe ellipse becomes more acute, as the water depth decreases as does the wavelength.

The steepness of the wave increases until the upper part spills over, or plunges over. At the

plunge line

, the depth of water and the height of the wave are almost equal.

The water which rushes up the beach is called the

swash

, and the water retuning on the surface is called the

backwash

.Slide15

Why a wave breaks:Slide16

Waves (continued)

Wave refraction

As waves approach an irregular coastline they are

refracted i.e. they become increasingly parallel to the coastline (best seen in a bay between two headlands)

The waves near the shore slow down due to frictional drag on the sea bed, whereas those in deeper water continue to move more quickly

This causes the waves to bend (creating curved

orthogonals

)

This process also creates

longshore (or littoral) currents

which carry sediment inshore from the headlandSlide17

Task: Draw an annotated wave diagram.Slide18

Plenary:

1)Draw an annotated wave diagram from memory that includes:

Wave height

Wave lengthCrest

TroughWave period

2) Swap diagrams and peer assess using the AFL sheet to help you set targets for improvement. Staple AFL sheet to diagram.Slide19

Defining ‘Coast’ and Waves

Lesson Objectives

1) Know what is meant by term the ‘coast’.

2) Understand waves.

Success Criteria

)Define ‘coast’.

2)Draw an accurate annotated wave diagram.Slide20

Wave Refraction and Tides

Lesson Objectives

1) Understand what wave refraction is.

2) Understand and be able to explain what different types of tide are caused by and their effects.

Success Criteria

1) Draw an accurate annotated wave refraction diagram.

2) Draw an accurate annotated tide diagram.Slide21

Starter:

What are the four most important things you remember about waves from last lesson?Slide22

Homework for next week!

Make revision cards on waves, wave refraction, tides, and storm surges for next week. Slide23

In small groups look at the wave refraction diagram and agree an explanation on what is happening to the waves and why? You have 5 minutes to prepare before feeding back.Slide24

WAVE REFRACTION

Effect of the sea floor on waves:

As waves approach the shore, their speed is reduced as they touch the sea floor.

Wave refraction causes two main changes:

The speed of the wave is reduced.

The shape of the wave front is altered.

If refraction is completed:

The wave fronts will break parallel to the shore.

Wave refraction also distributes wave energy along a stretch of coast.

On a coastline with alternating headlands and bays, wave refraction will concentrate destructive/erosive activity on the headlands, while deposition will tend to occur in the bays.

Land

Shoreline

Sea

Wave movement is slowed down in shallow water, and this causes the wave front to break

Faster movement in deep water causes waves to break parallel to each other

Depth decreasing onshore

Wind direction

Land

Sea

Dispersed energy

Concentrated

energy on

bank

Wave front

A

A

B

B

B1

B1

A1

A1Slide25

Draw and annotate a Wave refraction diagram:Slide26

Wave Refraction and Tides

Lesson Objectives

1) Understand what wave refraction is.

2) Understand and be able to explain what different types of tide are caused by and their effects.

Success Criteria

1) Draw an accurate annotated wave refraction diagram.

2) Draw an accurate annotated tide diagram.Slide27

Tides:

Tides are controlled by:

The gravitational effects of the moon (mainly) and the sun (partly), together with the rotation of the Earth.

The geomorphology of sea basins is locally significant

The moon pulls water to the side of the earth nearest to it, creating a bulge or

high tide

, with a complementary bulge on the opposite side of the earth

Intervening areas experience a

low tide

Spring tides

occur when the moon, the earth and the sun are in line (i.e. there is a new moon or a full moon)

Neap tides

occur when the moon, the earth and the sun form a right-angle (i.e. there is a half-moon)Slide28

Tides diagram:Slide29

Tides (continued):

Coriolis force

(the effect of the earth’s rotation) is also significant – it causes flows of air/water to be deflected to the right in the northern hemisphere. Tides flood around the British Isles in a clockwise direction

The

tidal range is also

affected by the morphology of the coastline and the sea bed

Where water is funnelled the tidal range will be higher (Severn estuary = 13m – a

macro-tidal

environment) and extreme narrowing of estuaries can cause a

tidal boreSlide30

Tides (continued):

Small enclosed seas only have a minimal tidal range such as the Mediterranean (0.01m – a

micro-tidal

environment)

The offshore gradient will control the extent of the inter-tidal zone. Steep gradients have a small inter-tidal zone whereas shallow gradients have a large inter-tidal zoneSlide31

Tides (continued):Slide32

Storm surges:

Storm surges

are rapid rises in sea level which are caused either by

intense areas of low atmospheric pressure and/or

severe onshore windsThey pose a major natural hazard on densely populated coastlines

Two areas which are particularly prone are the

southern North Sea

(depressions) and the

Bay of Bengal

(tropical cyclones)Slide33

Storm Surges - Case Study:

North Sea, 31

st

January-1st

February 1953:A deep depression (976mb)

moved over the North Sea

Intense low pressure caused the

sea level to rise by 0.5m

Gale force onshore winds

produced

waves over 6m

high

Water piled up in the southern North Sea

This event coincided with a

Spring Tide

– up to 2.5m in the Thames estuary

Rivers

discharging into the North Sea were at

flood level

264 people drowned in SE England

, 1835 in the NetherlandsSlide34

Plenary:

Draw and annotate a Tides diagram:Slide35

Wave Refraction and Tides

Lesson Objectives

1) Understand what wave refraction is.

2) Understand and be able to explain what different types of tide are caused by and their effects.

Success Criteria

1) Draw an accurate annotated wave refraction diagram.

2) Draw an accurate annotated tide diagram.